An angular uncomformity in eastern Nevada, just north of I-80 on the west side of the NV tunnel. (That's almost all of the cardinal directions in one sentence!) Here the lower sediments - the brown ones - were deposited and then tilted to about 45 degrees to form mountains hundreds of millions of years ago. Erosion flattened those mountains, and then the gray sediments were deposited on top - the gray was then horizontal. Next, more crustal folding - probably in the Mesozoic, the age of dinosaurs - pushed them up to their current angle and shoved the underlying brown strata up to the near vertical. (Basin and range faulting has not affected this particular area too much, according to McPhee.)
Jeb Butler